tcp and rtp header-compression over Ethernet

Unanswered Question
Apr 27th, 2008

I would like to know how I can use the command 'ip tcp header-compression iphc-format' and 'ip rtp header-compression iphc-format' on an Ethernet interface. I am trying to compress the header traffic when it is going through the Ethernet interface.

I have manage to compress the traffic over Serial interface (see below) but I don't know how it is done when it comes to Ethernet.

Compression over Serial ---->>>

interface Multilink1

bandwidth 64

ip address 10.130.60.1 255.255.255.252

max-reserved-bandwidth 85

service-policy output VOICE-POLICY

ip tcp header-compression iphc-format

no ip mroute-cache

no cdp enable

ppp multilink

ppp multilink fragment delay 10

ppp multilink interleave

ppp multilink group 1

ip rtp header-compression iphc-format

!

interface Serial1/0

bandwidth 64

no ip address

max-reserved-bandwidth 85

encapsulation ppp

no ip mroute-cache

keepalive 2

no fair-queue

ppp multilink

ppp multilink group 1

!

Thanks.

I have this problem too.
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tredgrove Mon, 04/28/2008 - 05:50

Pretty sure it is only supported for the following: serial lines using Frame Relay, HDLC, or PPP encapsulation. It is also supported over ISDN interfaces. Really intended for low bit rate links where the processing overheads of compression pay off. If your Ethernet is highly utilised and you are looking for assurance on specific traffic you could use a policing QoS policy. hope this helps.

I believe what you are trying to do is only supported on a true routed interfaces such as serial links, frame, isds, etc. The reason why I say true routed interfaces is because even if you turn a switch port into a routed port on a layer 3 switch I do not think this can be done. As the previous person said this is usually done on slow wan links such as frame circuits <384k where RTP and TCP header compression really helps.

Hope this helps.

Mark

blakearussell Wed, 04/30/2008 - 14:01

I don't believe you can do this on ethernet interfaces and even if you were able to find an ethernet interface which allowed you to compress the header it would take longer to compute the compression than to just transmit the frame with an uncompressed header.

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